Quality control of drug substances is an essential feature in the global marketplace to support public health and safety. To ensure compliance, regulatory bodies such as the U.S. Food and Drug Administration (FDA), typically monitor and hold pharmaceutical companies to certain standards. One important standard that is imposed on pharmaceutical companies by the FDA is the use of protocols described in the United States Pharmacopeia (USP).
USP establishes documentary standards in the form of monographs to establish product safety, sterility, strength, quality, purity and overall consistency. Monographs typically include the name of the ingredient or preparation, the definition, packaging, storage, label requirements, and the specification. The specification consists of a series of tests, procedures for the tests, and acceptance criteria, to which medicinal ingredients and products will have the stipulated strength, quality, and purity if conformance to the requirements in the monograph is met.
Ondansetron is a serotonin 5-HT3 receptor antagonist used to prevent nausea and vomiting that may be caused by medicines or radiation therapy. In addition to its therapeutic properties, ondansetron is particularly interesting from an analytical standpoint because, while monographs for quantitative determination of ondansetron provide strict limits on purity, separating ondansetron from its also highly polar related impurities, particularly 2-methylimidazole and imidazole, is challenging. For example, the difference in retention time between Impurity C and Impurity D from the reverse phase High Performance Liquid Chromatography (HPLC) set forth in the USP monograph is only two one hundredths of a second (0.02 seconds) difference. See e.g., USP monograph. Yet, the total combined limit for these impurities is 0.3%. Similarly, there is only five one hundredths of a second (0.05 seconds) difference in retention time between 2-methylimidazole and imidazole, and only a tenth of a second difference in retention time between ondansetron and impurity A. See id. Yet, the total combined limit for these impurities is 0.6%.
Because strict compliance with these mandated impurity limits is necessary to support the safe use of ondansetron, one problem has been how to identify and effectively separate ondansetron and its impurities from a sample in a reproducible manner that is suitable for high throughput quality control analysis. Several methods have been attempted, but require the use of ion-pairing, utilize more elaborate column materials (e.g., non-traditional silica bonded phases such as zirconium oxide or porous graphitic carbon), are not compatible with mass spectrometry, utilize high buffer concentrations and long equilibration times, or do not optimally separate the ondansetron impurities. See e.g., Research Journal of Pharmaceutical, Biological and Chemical Sciences, May-June 2014, 5(3) Pages 51-62; Alam Imran et al., International Research Journal of Pharmacy 2012, 3(2), pages 111-113; and Roemling et al., TOSOH Bioscience Application Note A08L16A.
Given the importance of quality control of drug substances in the marketplace, the need remains to develop a reliable high-throughput method for optimally separating the highly polar anti-nausea and anti-vomiting therapeutic ondansetron and its related impurities.